The present patent document relates to coherent combination of received ultrasound signals. In particular, coherent combination of receive data is provided for retrospective dynamic transmit beamformation.
Conventionally to generate a two-dimensional image, acoustic energy is transmitted along a plurality of scan lines sequentially. The transmit beam is focused at one location along the scan line. In response to each transmission, echo signals are received along the respective scan line. The receive beam is dynamically focused as a function of depth (time) along the scan line. Transmit focus is static, and receive focus is dynamic.
For more rapid acquisition, particularly for three-dimensional imaging, a broader transmit beam is formed. Echoes are dynamically received along a plurality of scan lines in response to the broader transmit beam. However, beam group artifacts and loss of signal-to-noise-ratio (SNR) may result. For greater numbers of receive beams formed for each transmit beam, a greater beam group artifact and a greater loss of SNR may result due to the static transmit focus.
Phase alignment and coherent processing of the receive data may reduce the beam group artifact. Coherent receive data representing the same locations but from two spatially adjacent transmissions are phase aligned to account for the difference in transmit focus. The phase alignment is based on the position of the transmit focus. After phase alignment, the data representing the same locations is then coherently combined.
The number of acquisitions may be reduced by interpolating data along scan lines. Received data representing different scan lines is phase aligned and combined to represent an intermediary scan line. However, artifacts due to the static transmit foci may still result.